Upon starting an internal combustion engine, several factors are frequently used to determine the correct fuel amount for accomplishing efficient combustion in the engine.
Temperature-related factors that most commonly influence the fuel amount required for efficient combustion include temperature of fuel, temperature of the air and engine components in the injection path, and temperature inside the combustion chamber. Whereas these temperature-related factors are not usually measured, intake air temperature and engine coolant temperature are measured and assumed to be closely related to the above items when the engine is running.
In a case where an engine has been shut off for a substantial period of time, temperatures within the engine attain equilibrium. For cases where the engine is restarted after being shut off for a fairly short period of time, temperature equilibrium is assumed not to have been attained. In such case, determination of a correct amount of fuel for injection into the engine for efficient combustion is difficult.
Attempts to use intake air temperature and engine coolant temperature to estimate fuel requirements can cause too much fuel to be estimated for delivery into the engine by the injector. This is because the localized temperatures in the fuel injection region and in the combustion chamber are typically higher than the engine coolant temperature following situations where the engine has only been shut off for a short period of time.
Methods currently exist that use combinations of factors to increase the accuracy of estimating the amount of fuel to be delivered to the internal combustion engine. These factors illustratively include engine running time, engine off time, last coolant temperature before engine shut down, and coolant temperature at starting of the engine. Using combinations of these factors, it is possible to determine if an engine is being started after a long or short period of soaking. However, it is appreciated that such methods require the use of special purpose sensors or transducers which adds time and cost to vehicle development and under some circumstances have are unable to deliver the most efficient amount of fuel to the engine.
The present invention proposes a method that utilizes the air/fuel ratio sensor heater conductance in conjunction with measured engine parameters to determine when an engine has been shut off for a short period of time thus allowing for the vehicle control system to estimate the correct amount of fuel to be delivered to the engine to accomplish efficient combustion.